Transducer with improved signal winding



Jan. 29, 1963 J. H. MOORE 3,076,137

TRANSDUCER WITH IMPROVED SIGNAL WINDING Filed April 10, 196]. 3 Sheets-Sheet 1 Amplifier l I i Ampllfler and Recmler Fig.

Jan. 29, 1963 J. H. MOORE 3,075,137

TRANSDUCER WITH IMPROVED SIGNAL WINDING Filed April 10, 1961 s Sheets-Sheet 2 Fig. 3 H

Jan. 29, 1963 J. H. MOORE TRANSDUCER WITH IMPROVED SIGNAL WINDING 5 Sheeis-Sheet 3 Filed April 10. 1961 IIIIIIIIIIIII:

3,076,137 TRANSDUCER WITH IMPROVED SIGNAL WINDING John H.,Moore, Havertown, Pa., assignor to Leeds and Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Apr. 10, 1961, Ser. No. 102,027 12 Claims. (Cl. 323-89) and an output current for producing a rebalancing M.M.F. -z

To detect an unbalance of these M.M.Fis, it is necessary to use a signal winding. In the aforesaid application the feedback and signal windings were both placed on the pole pieces. However, with such an arrangement it is difiicult to balance out unwanted out-of-phase components in the A.C. signal and there is considerable phase shift in the signal voltage when the ambient temperature changes, with consequent change in the effective gain and overloading of the amplifier. Additionally, the relative locations of the feedback and signal windings on the poles changed the phase of the signal and in some cases produced a very small signal. Additionally when the pole pieces were made of metal, the usable voltage output of the signal winding was substantially reduced.

The present invention avoids the undesirable phase shifts in signal voltage caused by the proximity of the feedback and signal windings and permits the use of the metal poles providing a very high permeability magnetic path together with increased mechanical strength and simplicity of manufacture without the foregoing disadvantages.

In accordance with the present invention there is provided a transducer having a magnetic circuit including ring structure and a pair of pole pieces extending perpendicular to the plane of the ring structure. The pole pieces are adapted to pass a magnetic flux through the ring structure and a saturating winding is wound on the ring structure with the latter serving as a core for the saturating winding. The transducer includes a signal winding with means for supporting the signal winding in encircling relation to the ring structure and between the poles. The saturating winding is symmetrically disposed on opposite sides of the ring structure and is symmetrical with respect to the signal winding for substantially zero coupling with the saturating winding. A resistance means is connected across a portion of the saturating winding further to reduce any remaining coupling to zero. The signal winding is electrostatically shielded from the saturating winding to reduce the undersirable capacitive coupling between the two windings. In the preferred form of the invention, the pole pieces are made of metal to provide a high permeability magnetic path with improved mechanical strength and the ring structure is made of a f-erro-magnetic material having lower eddy-current losses than the metal pole pieces, such for example as ferrite, the signal winding thus encircling a section of the magnetic circuit having a low loss. Such ferrites, in general, are manufacturing by sintering together a mixture of constituents containing an iron compound and one or more further metal compounds, as for example, a mechanical mixture of metal oxides. Such magnetic members contain no metal particles and provide the advantage of poor United States Patent 0 "ice electrical conductivity which reduces eddy current losses to a negligible value, while retaining the desired magnetic characteristics.

For a more detailed disclosure of the invention and for further objects and advantages thereof, reference is to be had to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a recording system utilizing a transducer embodying the present invention;

FIG. 2 is a diagrammatic view useful in describing the operation of the transducer in FIG. 1;

FIG. 3 is an elevation view partly in section of a transducer embodying the present invention;

FIG. 4 is a side elevation partly in section and looking in the direction of the arrows 4-4 in FIG. 3; and

FIG. 5 is a sectional view of the signal winding and saturating core, taken along the lines 5-5 in FIG. 3.

Referring to 'FIG. 1, there is schematically illustrated an electrical rebalancing recorder which includes as a portion thereof a transducer 10 embodying the present invention. The magnetic circuit for the transducer 10 comprises a saturable core in the form of endless ring structure 11 having a pair of pole pieces 13 and 14 extending perpendicular to the plane of the ring structure 11. The pole pieces 13 and 14 are adapted to pass a mag netic flux through the ring structure 11. A saturating winding 12 is wound on the ring structure 11 with the latter serving as a core for the saturating winding. As may be seen in FIG. 1, the saturating winding 12 is symmetrically disposed on opposite sides of the ring structure 11. A signal winding in the form of an A.C. output winding 17 encircles the ring structure 11 and is positioned between the poles 13 and 14 and at right angles to a line through ahe faces of the poles for substantially zero coupling with the saturating winding 12. The signal winding 17 is carried by non-magnetic support structure 63 as later to be described in connection with FIGS. 3-5.

As shown in FIG. 1, the saturable core 11 is in the form of a ferrite toroid. It will be noted that the saturable core 11 has a pair of bosses or enlargements 11a of cross section of the ring on opposite sides thereof at the areas where the ends of pole pieces 13 and 14 engage the ring 11. These bosses 11a provide an increase in mechanical strength and also provide an area adjacent the pole pieces having less flux density than the remainder of the ring 11 and thus less tendency for the flux to cross the air gap into the end of the respective pole pieces 13 and 14. This construction minimizes the passage of stray flux from the ring into the pole pieces and eliminates spurious responses of the sensor due to changes of the air gap between the pole pieces and the ring 11 which might be introduced by ambient temperature changes or other conditions encountered in normal operations. The saturating winding 12 is divided into two coils, 12a and 12b, on opposite sides of the ring or toroid 11. Therefore, if the coils 12a and 12b of the saturating or toroid winding are identical, there exists zero net flux linkages between the saturating winding 12 and the signal winding 17. To compensate for unsymmetrical variations in permeability and/or cross-sectional area of the material of the ring 11, a resistor 3 is connected in shunt across one coil of the saturating winding 12. In FIG. 1, the resistor 3 is shown connected across the coil 12a of winding 12. By adjusting the value of the resistor 3, the sum of the induced voltages in winding 17 from the two coils 12a and 12b of the saturating winding 12 can be made small enough to be disregarded. The error flux produced by the permanent magnet probe 31 passes through the two halves of the saturable core 11 which carries the respective coils 12a and 12b and the reluctance of the core 11 is periodically varied by high-frequency current. Thus, there is induced an A.C. voltage in the signal winding 17 in the same manner as when the signal winding rectifier schematically indicated by rectangle 20. One

winding 23 is divided into four parts or coils, 2312-2341, two of which are on pole 13 andthe other two on pole 1-4. The resistor 16 iseonnected to the top end of coil 2 3aand to the bottom .endof coil23c, the other ends of coils 23a and 230 being connected to eachother. The lower end of coil 23cis connected to the upperend of coil 23d which in "turn is, connected in series with coil 23b, thelatter being connected byway of conductor 22 to one side of aload resistor 24. The-other -side of the load resistor 24 is connected by way of conductor 25 to the other side of the outputof the RF amplifierand synchronous rectifier 20. The Isaturatingwinding '12 is connected to the oscillator 27 whieh is connected by way of conductors 28 and 29 to the synchronous rectifier portion of rectangle 20. The electrical circuits of the RF amplifier and syn.- chronous rectifier illustrated as rectangle 20 and the type .and may be of the type illustrated in the aforesaid copending application of McAdam, Serial No. 101,736.

The input means for producing an M,M.F. to establish a variable flux level in the magneticcircuit has been illus, .trated in the form of a permanent magnet probe 31 which ispositionedbetween the ends of the po es 13 and 14 and is movable along the longitudinal axis between the pair of poles in accordance with a-mechanical input signal such a f em B u dq tu e a d aph m a m t r or th suitable positioning means. The flux from the movable permanent magnetipmbe 31 balanced by the flux gen- 18 erated fromthe direct current feedback winding 23. In

order to have zero feedback current correspond. to a predetermined reference position of the permanent magnet probe 31, the poles 13 and 14 are each provided with bias means to. provide a magnetic bias opposing the flux from the permanent magnet probe 31. Various bias arrangernents may be employed, as disclosed and claimed in the aforesaid copendingapplicationofMcAd-am, Serial No. 1O1J 6- ne qfsuc ar neemems disclQ qdby-.M dam i tbfs r -th masn i b or t e ragsdu r by t e Sa gr n n lm n t 31 wh produces th pos on o ni ut n g mat q Y th method g sbia ns i i possib qjre use he tegp r u e efie ts to a ts/{small value w ou a s e m nsa on o e p rman nt mag t 3 As maybe. seen in FIG. 1, each of the poles Band 14 isprofvided with bias means in the for a of helical-shaped extensions 13b and 14b. The extensions 13b and 14b are of a high permeable material, such for example as HY-MU-SO which is a nickel-molybdenum-iron alloy manufactured by Carpenter Steel Co. This material has a high permeability at low flux densities and has a low coercive force. Each of the extensions 13b, 14b project from the respective one of the pole pieces 13 and 14 and extend around opposite sides of the longitudinal axis between the pair of pole pieces with the distal ends of the extensions 13b and 14b being directly opposite each other 3b. at 14. a tied by th rn o m a t flux n t gai s p me and 14b are so shaped that the by the lower ends of the bias extensions 13b and 14b and the poles 13 and 14 is identified by the symbol 4: The flux traversing the poles 13 and 14 and the saturating ring 11 is identified by the symbol 11 The bias extensions 13b spaced locations on the aid each other in producing circulating flux through the bias extensions and their associated air gaps. The flux a is the algebraic sum of the flux 4;; and 415. Thus whenqb is equal to the 15 is zero. The bias extensions 13b and 14b are arranged so that this condition occurs for the reference or zero position of the magnet probe 31. For any, other position of the magnet probe 31, will be either greater or less than and thus 5. will have a corresponding magnitude and direction.

As shown in FIG. 2, the permanent magnet probe has a leng th.substantiallygreater than the length of the bias extensions 13b and 1417 along the axis .of the transducer. In this arrangement, the flux o is derived from the central portion-of the permanent magnet probe 31 and is thus independent of the magnet position. 'The flux ,cp is derived from the lowerend of the permanent magnet probe. 3i1and varies linearly with magnet position. Asmay be. seen in FIG. 1, spaced stop members 34 are positioned'on opposite sides of a projection 31p carried by probe 31 so that the fringing fields at the distal and proximal ends of the probe 31 always operate in uniform ,inagnetic environments to provide linearity. The stops 34 limit motion of the distal end of the probe 3-1 between the poles 13 and 14 and prevent this end of the probe 31 from approaching the ends of the poles by a distance less than the length of the air gap therebepermanent magnet 331 soft iron pole pieces 31b which are disposed on opposite sides of the permanent magnet core 310 and insure a uniform {diStIlblltlOIlOf magnetic flux along the length of the probe 31 to further insure linearity between the changeof flux in theppoles and extensions and displacement of the probe 31.

-While the permanent magnet probe 31 has been illusated in FIG. Zasbeing much longer than the axial length of the hellical-shaped extensions 13b and 14b, it isto be understood that-the probe may be shorter than shown and that the upper end of the probe 31 may termin e a t dott d l tr 1. th h n merit, the fiuxes introduced into the magnetic circuit th lifl i fient magnet probejli This latter arrange ment provides increased-sensitivity for the transducer 10.

In theelectrical rebalancing recorder shown n FIG. 1

concurrently by means of the threaded drive 47 moves the magnet'probe 31 along I v the pair of poles 13 and 14 against the bias of a spring 48. The spring 48 is utilized to eliminate the effects of backlash or lost motion in the mechanical drive from the motor 44 to the probe 31.

Upon change in the axial position of the permanent magnet probe 31, by rotation of the balancing motor 44 but without rotation of probe 31, the M.M.F. introduced into the magnetic circuit by the lower end of probe 31 will be ehanged -producing a net flux which is other than zero and producing an A.C. signal as a result of periodic saturation of the saturable core 11 by the winding 12. The A.C. signal from winding 17 is applied to the input of the RF amplifier and synchronous rectifier 20, the output of which is connected to the feedback winding 23 and to the resistor 24 which is in the input circuit of the recorder to produce a rebalancing electrical feedback signal. When the rebalancing electrical feedback signal is equal to and opposite from the unknown electrical signal E the rebalancing motor 44 will stop and thus the index and pen assembly 46a will be positioned relative to the chart 46c and scale 46s as determined by the magnitude of the signal E The span-setting resistor 16 provides a means for adjusting the relation between the magnitudes of input signals E and the corresponding displacements of the pen index assembly 4611 from its zero signal position. It thus provides adjustment for the magnitude of E corresponding to full-scale displacement of the pen index assembly, i.e. the span of the recorder. Span adjustment is effected by changing the position of adjustable contact 16a along span-setting resistor 16 to alter the fraction of the D.C. output current from the synchronous demodulator which flows in the pair of feedback coils 23a, 23c. Coils 23a and 230 are connected so that they are series aiding to produce flux in one direction in the magnetic circuit including poles 13 and 14 and the saturable ring core 11. Coils 23b and 23d are connected so that they are series aiding to produce flux in the opposite direction to that produced by coils 23a and 23c. When adjustable contact 16a. is at the lower end of resistor 16, all the D.C. output current flows through coils 23b and 23d and no opposing is produced by coils 23a and 23c. With this adjustment, the direct output current has maximum effectiveness in producing to balance the of the magnet probe 31. The output current necessary to develop the balancing electrical signal across resistor 24 required by an input signal E is thus produced by a relatively large displacement of the magnet probe and the pen-index assembly from their zero reference positions, i.e., the recorder span is minimum. Adjustment of contact 16a upward to a new position on resistor 16 causes a fraction of the D.C. output current to flow through coils 23a and 230. With this adjustment, an M.M.F. is produced by coils 23a and 23c to oppose the balancing M.M.F. of coils 23b and 23d, thus reducing the effectiveness of the output current in balancing the of the magnet probe when the probe is displaced from its zero-reference position. The output current necessary to develop the balancing electrical signal across resistor 24 required by an input signal E is now produced by a relatively smaller displacement of the magnet probe 31 and pen-index assembly 46a from their zero-reference span of the recorder has been increased. Span-adjusting resistor 16 can readily produce span adjustments having ratios of 4:1. Other methods of span adjustment based on controlling the effectiveness of the output current in producing balancing are possible. Simple shunting of the feedback windings by an adjustable resistor is one such method; however, with this method ratios as large as 4:1 in span adjustment are not as easily obtained. Magnetic shunts on the magnetic circuit of the transducer can also be used for span adjustment. Span adjustment over large ratios can also be obtained by a different method by making resistor 24 adjustable. The span adjustments do not affect the zero-reference position of the magnet probe 31 and pen-index assembly 4611.

Associated with the span-adjusting resistor 16 there may be provided resistance means for varying the span of the sensor with changes of ambient temperature to compensate for the effects of ambient temperature changes on other elements in the system. In the system of FIG. 3 there has been shown a shunting resistor which may positions, i.e., the

t 6 be provided with a temperature coefficient to effect the desired temperature compensation.

Adjustment of the position of pen-index assembly 46a relative to chart 46c and scale 46s for zero input signal can be provided by a second permanent magnet which is adjustable in position relative to the magnetic circuit containing poles 13 and 14. One arrangement is illustrated by zero-adjusting magnet 77 in FIG. 3. Permanent magnet 77 is arranged with north and south poles as indicated by N and S respectively, and is mounted by a screw 78 operating in a fixed support 79 so that it can move in its axial direction. The of magnet 77 produces a relatively small flux in pole extensions 13b and 14b which can aid or oppose the flux produced by magnet probe 31 in pole extensions 13b and 14b, depending upon the adjustment of screw 78. The relatively small flux in pole extensions 13b and 14b from magnet 77 therefore can eifectively increase or decrease the biasing effect of magnet 31 which establishes the zero-reference position of magnet probe 31 as explained above. As screw 78 is advanced, the north pole N of magnet 77 is moved closer to pole extension 14b. It is also moved closer to pole extension 13b, but for the first part of its travel it remains at a relatively great distance from pole extension 13b. Flux is thus produced by magnet 77 in pole 14b in the same direction as the flux produced by magnet 31 and the biasing effect is increased. This requires that the lower end of magnet 31 move downward into greater engagement with poles 13 and 14 to produce Zero net flux in these poles, i.e., the Zero reference position of magnet 31 and pen-index assembly 46a has been moved upscale. Further adjustment of screw 78 to move magnet 77 toward the axis of the transducer increases the upscale displacement of the Zero-reference position until at one position of magnet 77, the upscale displacement is maximum.

Continued adjustment of the position of magnet '77 toward the axis of the transducer brings its north pole toward a position adjacent the part of the pole extension 14b which is parallel to the motion of magnet '77. As magnet 77 approaches this position, the distance of its north pole N from pole extension 1412 becomes relatively independent of the position of the magnet, while the distance of its north pole N from pole extension 13b is still strongly dependent on the magnet position. Therefore, as magnet 77 is moved toward the axis of the transducer from the point of maximum upscale Zero-reference position, the flux from its north pole N into pole extension 13b increases more rapidly than that into pole extension 14b. The net flux in pole extensions 13b and 14b from magnet 77 is thus reduced and the eifective bias is reduced. The zero-reference position is moved downscale from its maximum upscale position. Still further adjustment of magnet 77 toward the axis of the transducer will cause magnet 77 to approach a position in which its south pole S is closer than its north pole N to pole extension 141), while its north pole is closer than its south pole S to pole extension 13b. When this condition is reached, the elfect of magnet 77 is to decrease the effective bias by introducing flux in pole extensions 13b and 14b which opposes the flux from magnet 31. As the effective bias is decreased by further adjustment of magnet 77 in the same direction, the position of the lower end of magnet probe 31 for zero net flux in poles 13 and 14 moves upward into less engagement with poles 13 and 14. The zero-reference position of pen-index 46:: may

thus be moved downscale beyond the position it would occupy if no zero adjusting magnet 77 were present.

Zero adjustment can be provided by other methods as for example by passing a stable adjustment current through a winding on poles 13 and 14. Such zero adjustments have no effect on the span.

Referring to FIGS. 3 and 4, there is illustrated a commercial form of the transducer 10 embodying the principles schematically illustrated in FIGS. 1 and 2. As

may be seen in FIGS. 3 and 4, the transducer 10 is proded with a housing :38 which is adapted to be supported at its lower end by a member 51. At the other end of the housing 50 there is provided a plate member 52 which is connected to the housing -8 by screws 53. The plate 52 supports in depending relation disc 54 by means of connecting posts 55. The disc or support 54 in turn has connected thereto rod members 56 which support a lower disc member 57. The disc members 54 and 57 cooperate to support the pair of poles 13 and 14 the upper ends of which are provided with the helical-shaped extensions 13b and 14b, FIG. 3. n the preferred form of the invention, the poles l3 and 14 and their respective extensions 13!) and 1% are of one-piece construction of high permeable metal. at low flux densities, such for example as HY-MU-SO. This construction is preferred to that where the poles are of .ferriteand the extensions are of metal, as such construction tends to induce strains resulting from assembly and ambient temperature changes frequently cause the ferrite poles to break. :In the present invention, locating the signal winding 17 about a section of the magnetic circuit containing the low-loss saturable core 11 of ferrite, there is avoided undesirable phase shifts in signal voltage otherwise caused by the proximity of the feedback and signal windings and at the same time there is gained the advantage of metal poles.

As may be seen in FIGS. 3 and .4, the bosses 11a of the saturating ring 11 of ferrite, which carries the saturating winding 12, are held against the lower ends of the metal pole pieces 13 and 14 by means of a supporting member 59 which is held in place by a retaining member 60 secured to the disc 57 by screws 61. The support 59 also supports the coil form '63 for the AC. output winding 17 which is provided with electrostatic shielding62. As may be seen in FIG. 5, the coil form is made from an electrical insulating mater al, such for example as one of the plastics which is readily molded into the desired rectangle shape shown in FIG. 3. The plastic form 63 is then provided with a layer of metal foil 62 which acts as an interior electrostatic shield for the winding 17. On top of the layer of foil 62 is a layer of electrical insulation, such for example as electrical tape 64 and on top of this is a single layer winding comprising a plurality of turns and which forms the output winding 17. The top of the winding 17 is covered with another layer of electrical insulating tape 64 and on top of that is placed an outer layer of metal foil 62 for exterior electrostatic shielding. The output winding assembly, including the winding 17 and the coil form 63;,

is adapted to be held in position between the poles 1 3 and 14 by means of a plurality of clip. members 58 and rivets 6-9. The winding 57 is so positioned that it is symmetrical with the sections of the saturating winding 12 on the saturable core 11.

The pole pieces 13 and '14 :are provided with their respective coils 23a-d. A well 65 is positioned along the longitudinal axis of the poles 13 and 14. The well 65' is adapted to receive the permanent magnet probe 31 for movement along the longitudinal axis in response to an input signal movement. The probe 31 does not rotate, but instead moves in the manner of a plunger. When the probe is to be moved in response to a primary quantity, the probe 3-1 may be sealed within an enclosure 66, which may be pressurized, to eliminate the mechanical motion through a upper end of the enclosure 66 is threaded at 66a and is adapted to be received in a correspondingly threaded opening in a housing 67 of the primary motion-producing device. The housing 50 of the transducer may aditionally be secured to the housing 67 by screw 68.

The lower end of the transducer 10 is provided with a contact block 70 which is secured to the housing 59' by a plurality of screws 71. The contact block 79 is made from electrical insulating material and supports a plural- .pressurized wall. The

necessity of transmitting ity of contact members 72 around its circumference. The contact members 72 are separatedfrom each other by projections or rib members 70a which extend radially about the center of the contact block 70. The contact members 72 have one end which extends inside of the housing for electrical connection with the coils 23a-d and windings 12 and 17. The opposite ends of the contact members 72 are adapted to receive screw members 73 for connection of external leads illustrated by the lead 74 in FIG. 3. These leads are connected to the other elements of the electrical circuit disclosed as blocks in FIG. 1.

As may be seen in FIG. 3, there 76 which extends through the side 50 for the transducer and supports within the housing a permanent magnet 77. The permanent magnet 77 is relatively short and is positioned over the helical-shaped extension 14b with the north pole end of the magnet 77 adjacent the well for receiving the probe 31. As may be seen in FIG. 4, the magnet 77 is positioned at right angles with respect to the permanent magnet probe 31. The magnet 77 is adjustably positioned by means of the holder 76 and is utilized to adjust the zero or reference position of the probe 31 of the transducer 10 or to adjust the output current fora particular position of the probe 31. The adjustable magnet 77 corrects for small variations in the reference position arising from manufacturing tolerances of both the transducer and the input device.

From the foregoing description it will be seen by positioning the signal winding around the saturable core and away from the pole pieces which carry the feedback winding, it is possible to balance out unwanted out-ofphase componentsin the AC. signal with relative ease. There has also been eliminated the considerable phase shift in the signal voltage when the ambient temperature changes that is present when the feedback Winding .23 and the Signal winding 17 are located adjacent each other. The present invention also enables the use of metal pole pieces which may be made integral with the helical-shaped extensions, thus providing for ease in the same time eliminating breakage of the poles which resulted when the latter were made of ferrite. When the pole pieces are made from metal, it is not possible to place the signal winding on them as under such conditions the usable voltage output from the signal Wll'ldlIlgWlll be very-small and at an unusable level as theeddy-current losses in the relatively highconductivity metal poles will absorb substantially all of the energyof the induced signal.

While .a preferred embodiment of the invention has been described and illustrated, it is to be understood that further modifications thereof may be made within the scope of the appended claims.

What is claimed is:

1. In a transducer having endless ring structure and a is illustrated a holder wall of the housing a magnetic circuit including pair of pole pieces extending of said ring structure, said ring structure with the latter serving as a core for said saturating winding, a signal winding, and means for supporting said signal winding in encircling relation to said ring structure and between said poles for substantially zero coupling with said saturating winding.

2. In a transducer according to claim 1 wherein resistance means is connected across a portion of said saturating Winding to reduce said coupling to zero.

3. In a transducer according to claim 1. wherein said saturating winding is symmetrically disposed with respect to said signal winding.

4. In a transducer according to claim 3 wherein said saturating Winding is disposed on opposite sides of said ring structure.

5,. In -a transducer according to claim 1 wherein said signal winding is electrostatically shielded from said saturating winding.

6. In a transducer according to ring structure is composed of ferrite.

7. In a transducer according to claim 6 wherein said pole pieces are made of metal.

8. In a transducer having a magnetic circuit including a pair of metal pole pieces, a saturable core ring positioned adjacent one end of said pair of poles in a plane perpendicular to the axis of said poles, said saturable core ring being of a material having lower eddy-current losses than said metal pole pieces, a saturating winding on said saturable core ring, a signal winding encircling said core ring, and means supporting said signal winding in spaced relation to said core ring and at right angles to a line through said pole pieces for zero net flux linkage between said windings.

9. A transducer according to claim 8 wherein said signal winding comprises a single layer winding including a plurality of turns on a non-magnetic form, said signal winding being electrostatically shielded both internally and externally, and said signal winding being arranged symmetrically and respect to said saturating winding.

10. In a transducer according to claim 8 wherein said saturable core ring includes portions of enlarged crosssectional areas adjacent said one end of said pair of pole pieces to minimize the passage of stray flux from said ring into said pole pieces and eliminate spurious responses of the transducer due to changes in air gap be tween said pole pieces and said ring.

11. A transducer having a magnetic circuit including endless ring structure and a pair of pole pieces extending perpendicular to the plane of said ring structure, said pole pieces being adapted to pass a magnetic flux through said ring structure, input means for producing an claim 1 wherein said to establish a variable flux level in said magnetic circuit, a saturating winding wound on said ring structure with the latter serving as a core for said saturating winding, a feedback winding wound on said pair of pole pieces, a signal winding, amplifying means having its input circuit connected to said signal winding and its output connected to said feedback winding, and means for supporting said signal winding in encircling relation to said ring structure and between said pole pieces at a location displaced from said feedback winding for substantially zero coupling with said saturating winding and for reduced electrostatic coupling with said feedback winding.

12. A transducer having a magnetic circuit including a pair of metal pole pieces, a saturable core ring positioned adjacent one end of said pair of pole pieces in a plane perpendicular to the axis of said pole pieces, said saturable core ring being of a material having lower eddycurrent-losses than said metal pole pieces, said saturable core ring having enlarged portions engaging the end of said pole pieces to reduce the flux density in said ring at locations adjacent said pole pieces, a saturating winding on said saturable core ring between said enlarged portions, a feedback winding on saidpair of pole pieces, a signal winding encircling said core ring, amplifying means having its input circuit connected to said signal winding and its output connected to said feedback Winding, input means adjacent the opposite ends of said pair of pole pieces for producing an to establish a variable flux level in said magnetic circuit, and means supporting said signal winding in spaced relation to said core ring and at right angles to a line through said pole pieces for zero net flux linkage between said signal and saturating windings.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noe 3,076, 137 January .29 1963 John Ho Moore It is hereby certified that error appears in the above numbered pat ent requiring correction and that the sa id Letters Patent should read as corrected below.

Column 1 line 68 for "manufacturing" read manufactured column 2, line 34 for "ahe" read the column 6 line 7O for "adjustment" read adjustable for "and" column 9 line .23 read with Signed and sealed this 10th day of December 1963,

SEAL Attest EDWIN L, REYNOLDS ERNEST W: SWIDER Attesting Officer A 'i fig Commissioner oi." Fawn UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,O76 137 January 29 1963 John Ho Moore It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 68 for "manufacturing" read manufactured column 2, line 34, for "ahe" read the column 6 line 70 for "adjustment" read adjustable column 9 line 23, for "and" read with Signed and sealed this 10th day of December 1963,

(SEAL) EDWIN La REYNOLDS ERNEST w. SWIDER Attesting Officer Acting Commissioner of Patents 

1. IN A TRANSDUCER HAVING A MAGNETIC CIRCUIT INCLUDING ENDLESS RING STRUCTURE AND A PAIR OF POLE PIECES EXTENDING PERPENDICULAR TO THE PLANE OF SAID RING STRUCTURE, SAID POLE PIECES BEING ADAPTED TO PASS A MAGNETIC FLUX THROUGH SAID RING STRUCTURE, A SATURATING WINDING WOUND ON SAID RING STRUCTURE WITH THE LATTER SERVING AS A CORE FOR SAID SATURATING WINDING, A SIGNAL WINDING, AND MEANS FOR SUPPORTING SAID SIGNAL WINDING IN ENCIRCLING RELATION TO SAID RING STRUCTURE AND BETWEEN SAID POLES FOR SUBSTANTIALLY ZERO COUPLING WITH SAID SATURATING WINDING. 